1. Technical Field
The invention relates generally to wellbore operations. More particularly, the invention relates to a method and an apparatus for actuating a movable member of a downhole device.
2. Background Art
Downhole devices that have slidable members and that are operable by actuating the slidable members are routinely employed for various wellbore operations. Examples of such downhole devices include ball, flapper, and sleeve valves. Typically, a shifting tool is run into the wellbore to engage the slidable member. Then, force is applied to the shifting tool to actuate the slidable member, e.g., by moving the slidable member along an axial axis of the wellbore. The shifting tool is typically lowered into the wellbore on the end of a coiled tubing or pipe. The stiffness of the coiled tubing makes it possible to apply weight to the shifting tool to actuate the slidable member. However, because the weight that can be applied to the coiled tubing is limited, the shifting tool may not have the necessary force required to move the slidable member, e.g., when debris is lodged in the path of the slidable member. In addition, mobilizing a coiled tubing is very expensive, and retrieving the coiled tubing after operating the downhole device will require either stripping the tubing out or killing the well, both of which are very costly operations. Therefore, it is desirable to have a reliable means of providing adequate force to actuate a slidable member of a downhole device. It is also desirable that this means for providing adequate force is cost-effective.